There are known methods of pumping liquids, particularly sewage, using at least one positive displacement pump operating tank, which take place in a sequence of two phases: in the filling phase, during which the liquid is admitted into the operating tank through a through and pneumatically controlled inlet valve in place of the gas removed from the tank until it is full; the pumping phase, during which the pneumatically controlled inlet valve located on the inlet of the operating tank is closed and then the compressed working gas is admitted into the tank, under whose pressure the liquid is displaced from the tank, until the tank is emptied.
Two methods of pneumatic inlet valve closing are substantially used.
The first one, commonly used, is the pneumatic control of a blade valve. This form of inlet valve pneumatic control makes it possible to avoid the use of large and uncontrollable hydraulic devices at the outset of the pumping phase, but a blade valve has a limited number of reliable work cycles. For this reason, designs are made for a small number of pumping cycles, and as a result large operating tanks which, in turn, leads a considerable increase of the volume of the operating chambers of such transfer stations, thereby greatly increasing investment costs.
The second commonly used method of controlling the inlet valve closure is closing the inlet valve using the compressed working gas pumped into the operating tank during the pumping stage.
The inlet valves used are, for example, ball float valve with a spherical float, as disclosed in the German patent description DE 100 20 359. These valves, however, can cause large uncontrolled hydraulic pressure waves and are not fully resistant to blocking with contaminants found in faecal sewage. In turn, clapper-type valves (particularly horizontal ones), though more resistant to blocking by contaminants found in faecal sewage, also generate large and uncontrolled hydraulic pressure waves. The noise caused by these spikes often eliminates the use of such transfer stations near residential areas. A structure, which limits the space requirements in a dry pumping station is presented in French patent description FR 2822484. This structure makes it possible to place a pneumatic positive pressure pump in a relatively narrow, prefab dry tank with a round cross-section. A solution is also known from Polish patent application P-382032 (WO 2007/108711 A1), which facilitates an even greater compaction of the pneumatic positive displacement pump in a narrow prefab dry tank with a round cross-section, due to the use of an external retention tank located outside of the dry tank, which has a volume in excess of the operating tank of the pneumatic positive displacement pump. For this reason, the operating tank may be several times smaller than a classic operating tank, and by the same token require a much smaller bottom surface area requirement in the dry tank for the installation of the pneumatic positive displacement pump. High reliability was achieved using elbow ball valves with a non-floating ball (as demonstrated in the European patent application EP 1860245), with an increased number of work cycles of the operating tank. The drawbacks of the abovementioned solutions described as the second method of closing the inlet return valves, are large and uncontrolled hydraulic pressure waves at the beginning of the pumping phase as a result of the introduction of compressed working air into the operating tank of the pneumatic positive displacement pump. These are very distinct when the working pressure exceeds 2 Bar.
Classic pneumatic positive displacement pump operating tank structures have large surface requirements at the bottom of the dry tank they are installed in, or require it to be greatly deepened which makes them vastly more costly to install.
Two basic operating tank structures are known.
The first consists of bottom-fed sewage inflow and outflow into and from the operating tank, which is used most frequently and disclosed in patent descriptions U.S. Pat. Nos. 1,594,483, 3,049,489, in the French patent FR 2822484 as well as in the Polish patent application P-382032 (WO 2007/108711 A1). The abovementioned structures are most preferable in terms of the minimal operating tank depth, which was described in American patent description U.S. Pat. No. 3,302,575 and in the German patent application DE 100 20 359. Such a construct is preferable in light of minimising the surface requirements of the operating, as described in the book entitled “Komunale Abwasserpumpwerke”; by Dieter Weismann—Polish translation, Warsaw, 2001, “Komunalne przepompownie ścieków”, edition Seidel-Przywecki Sp. z o. o.
Thus, a need arose for such a novel inflow valve closure control that would ensure the longevity of the control elements, simplicity of use and which would not cause problems with large and uncontrolled hydraulic pressure waves on the inflow valve.
A need has also arisen for the design of a new shape of the operating tank of the pneumatic positive displacement pump, which would minimise the surface area required by the pneumatic positive displacement pump on the bottom of the dry tank, and at the same time would not necessitate increasing the depth of the dry tank.
For the even more optimal use of the bottom of the dry tank, in order to install a device according to the present invention therein, use was made of the advantages of the solution described in Polish patent application P-382032 (WO 2007/108711 A1). This solution consists of the use of the increased capacity of an external pipe operating tank in relation to traditional solutions, and at the same time increasing the number of work cycles of the operating tank. The compressor, being the source of compressed air, powers on and off only after multiple operating cycles of the operating tank, until it empties the external operating tank of the pneumatic positive displacement pump, which lowers the number of power-on cycles of the compressor, and lowers energy usage.